Summary from the authors: What is responsible for genetic fragmentation? Spatiotemporally explicit model testing can help to reach the answer

An important task of conservation genetics is to determine whether spatial patterns of genetic structure were driven by historical processes of population isolation (e.g. the presence of natural barriers to dispersal) or if they are a consequence of human activities (e.g. habitat destruction and fragmentation). Resolving this question is not trivial and has important implications for establishing proper on-ground management practices: Do distinct genetic groups represent evolutionary significant units that deserve to be preserved or, on the contrary, is genetic fragmentation a consequence of anthropogenic habitat destruction and conservation actions should focus on restoring population connectivity? In this study, we used genomic data and a spatiotemporally explicit model-based approach to test these hypotheses in a red listed grasshopper endemic to the Iberian Peninsula. Our demographic analyses indicate that although natural barriers to dispersal (mountains) are the main factors determining spatial patterns of genomic variation in the study species, anthropogenic habitat destruction has also contributed to the genetic fragmentation of its populations. This study emphasizes the potential of model-based approaches to gain insights into the temporal scale at which different processes impact the demography of natural populations of great conservation concern. – María José González Serna, Personal investigador UCLM

Photo courtesy of Piluca Álvarez.

González-Serna, M. J., Cordero, P. J. and Ortego, J. 2019. Spatiotemporally explicit demographic modelling supports a joint effect of historical barriers to dispersal and contemporary landscape composition on structuring genomic variation in a red-listed grasshopper.Molecular Ecology, 28:2155-2172.

Summary from the authors: What do gut microbes do for their hosts?

Despite a flood of recent interest in this question for humans, the answer remains a mystery for the vast majority of animals. Gut microbiota are often assumed to provide nutritional benefits, but many insects acquire the majority of their nutrients during larval feeding, leaving less opportunity for bacterial contributions to adult nutrition. In fact, when food is scarce the adult gut flora might even impose a net reproductive cost.

Photo courtesy of A. Ravenscraft

We tested this prediction in the Mormon fritillary butterfly (Speyeria mormonia), a denizen of mountain meadows in the American Rockies. We experimentally subjected wild caught butterflies to a brief burst of antibiotics to disrupt their gut flora and then maintained them with either ad lib feeding or a 50% starvation diet. Contrary to our
predictions, the number of bacteria in the gut did not correlate with butterfly fitness even if the butterfly was starved, though a few individual bacteria species were associated with increased or decreased lifespan.

Overall, these results suggest that gut bacteria may have little net
effect on some animals. – Alison Ravenscraft, NIH PERT Postdoctoral Fellow, University of Arizona

Ravenscraft A, Kish N, Peay K, Boggs C. No evidence that gut microbiota impose a net cost on their butterfly host. Mol Ecol. 2019;28:2100–2117.

Summary from the authors: A reciprocal translocation radically reshapes sex‐linked inheritance in the common frog

Sex chromosomes evolve when recombination ceases between the X and Y chromosomes, and the X and Y chromosome accumulate differences between them. We examined sex chromosomes across three populations of the common frog, Rana temporaria. In one population, we confirm that the sex chromosome and an autosome have undergone a reciprocal translocation, a rearrangement in which two chromosomes swap arms. The resulting chromosome pair is coinherited as sex chromosomes. Furthermore, because frog chromosomes only recombine near the ends, much of the newly added chromosome is incorporated into the sex-determining region. This provides a large amount of new genetic material to the selective environment of the sex chromosomes, in which sequence on the X chromosome are under selection in females twice as often as males, and sequence on the Y are subject sex-specific selection in males. We further confirmed unique sex-chromosome arrangements in the other two populations, demonstrating that Rana temporaria has extensive structural polymorphism in its sex chromosomes. — Melissa Toups

Toups, M., Rodrigues, N, Perrrin, N, and M. Kirkpatrick. (2019). Genomics, environment and balancing selection in behaA reciprocal translocation radically reshapes sex‐linked inheritance in the common frog. Molecular Ecology28(8), 1877–1889.

Summary from the authors: Genomics, environment and balancing selection in behaviourally bimodal populations: The caribou case

Like people, caribou are individuals. Each animal has a different colouration pattern, size, metabolism and other characteristics. And each behaves differently, including in specific environments. But what drives such differences, or diversity, in caribou? Are such mechanisms similar in other animals, including people? And can understanding what gives rise to such diversity help conserve caribou, a threatened species in Canada, which recently became functionally extinct in the Lower 48 US? This study has identified a natural mechanism in caribou that preserves and ensures long-term genetic and behavioural diversity of the species in various habitats across western North America, from Alaska to the Southern Canadian Rockies. This mechanism, called “balancing selection,” has resulted in caribou populations having not only distinctly different genetic traits but also diverse and likely adaptive behaviours, including whether individual animals migrate or not. Balancing selection could ensure that two or more behaviours or characteristics are selected at the same time, by balancing the benefits of one type of behaviour or appearance with the benefits of other types. This research is the first genomic study of caribou and perhaps the first to confirm the gene-driven balancing selection mechanism in a wild species in nature. – Marco Musiani

Cavedon, M., Gubili, C., Heppenheimer, E., vonHoldt, B., Mariani, S., Hebblewhite, M., … Musiani, M. (2019). Genomics, environment and balancing selection in behaviourally bimodal populations: The caribou case. Molecular Ecology, 28(8), 1946–1963.